The present invention relates to medical devices and in particular to a medical device for automatically selecting stimulation chamber, or chambers, based on sensed cardiac signals.
When functioning properly, the human heart maintains its own intrinsic rhythm, and is capable of pumping adequate blood throughout the body""s circulatory system. However, some people have irregular cardiac rhythms, referred to as cardiac arrhythmias. Such arrhythmias result in diminished blood circulation. One mode of treating cardiac arrhythmias uses drug therapy. Drugs are often effective at restoring normal heart rhythms. However, drug therapy is not always effective for treating arrhythmias of certain patients. For such patients, an alternative mode of treatment is needed. One such alternative mode of treatment includes the use of a cardiac rhythm management system. Such systems are often implanted in the patient and deliver therapy to the heart.
Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via an intravascular leadwire or catheter (referred to as a xe2x80x9cleadxe2x80x9d) having one or more electrodes disposed in or about the heart. Heart contractions are initiated in response to such pace pulses (this is referred to as xe2x80x9ccapturingxe2x80x9d the heart). By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly.
Cardiac rhythm management systems also include cardioverters or defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Defibrillators are often used to treat patients with tachyarrhythmias, that is, hearts that beat too quickly. Such too-fast heart rhythms also cause diminished blood circulation because the heart isn""t allowed sufficient time to fill with blood before contracting to expel the blood. Such pumping by the heart is inefficient. A defibrillator is capable of delivering a high energy electrical stimulus that is sometimes referred to as a defibrillation countershock. The countershock interrupts the tachyarrhythmia, allowing the heart to reestablish a normal rhythm for the efficient pumping of blood. In addition to pacers, cardiac rhythm management systems also include, among other things, pacer/defibrillators that combine the functions of pacers and defibrillators, drug delivery devices, and any other implantable or external systems or devices for diagnosing or treating cardiac arrhythmias.
One problem faced by cardiac rhythm management systems is the treatment of heart failure (also referred to as xe2x80x9cHFxe2x80x9d). Heart failure, which can result from long-term hypertension, is a condition in which the muscle in the walls of at least one of the right and left sides of the heart deteriorates. By way of example, suppose the muscle in the walls of the left side of the heart deteriorates. As a result, the left atrium and left ventricle become enlarged, and the heart muscle displays less contractility. This decreases cardiac output of blood through the circulatory system which, in turn, may result in an increased heart rate and less resting time between heartbeats. The heart consumes more energy and oxygen, and its condition typically worsens over a period of time.
A deterioration of the heart""s conduction system often accompanies heart failure. Normally, intrinsic signals of the heart""s conduction system originate in the sinoatrial (SA) node in the upper right atrium. These signals travel through and depolarize the atrial heart tissue to trigger the contraction of the right and left atria. The intrinsic atrial heart signals are received by the atrioventricular (AV) node which, in turn, triggers a subsequent ventricular intrinsic heart signal that travels through the specialized conduction system (Purkinje Fibers) and depolarizes the ventricular heart tissue such that resulting contractions of the right and left ventricles are triggered substantially simultaneously.
In the above example, when the left side of the heart has become enlarged due to heart failure and the conduction system in the left ventricle is blocked, the ventricular intrinsic heart signals may travel through and depolarize the left side of the heart more slowly than in the right side of the heart. This condition is referred to as left bundle branch block (LBBB). As a result, the left and right ventricles do not contract simultaneously, but rather, the left ventricle contracts after the right ventricle. This reduces the pumping efficiency of the heart. Moreover, in the case of LBBB, for example, different regions within the left ventricle may not contract together in a coordinated fashion.
Heart failure can be treated by biventricular (or left-ventricular) coordination therapy that provides pacing pulses to both right and left ventricles. See, e.g., Mower U.S. Pat. No. 4,928,688. Heart failure may also result in an overly long atrioventricular (AV) delay between atrial and ventricular contractions, again reducing the pumping efficiency of the heart. Providing heart failure patients with improved pacing and coordination therapies for improving AV-delay, coordinating ventricular contractions, or otherwise increasing heart pumping efficiency continues to be an area in which improved techniques and therapy protocols are needed.
The present subject matter provides for improved pacing and coordination therapies for heart failure patients. The present subject matter includes a method and apparatus for recording intrinsic electrograms, including QRS complexes, of left and right ventricles. A timing relationship is then determined between the intrinsic electrograms of the left and the right ventricles. A selection of one or more ventricular chambers in which to provide pacing pulses is then made based on the timing relationship between intrinsic electrograms of the left and the right ventricles.
In one embodiment, determining the timing relationship includes calculating a delay between a left ventricular and a right ventricular sensed intrinsic ventricular depolarizations and measuring a duration interval of one or more QRS complexes. In one embodiment, intrinsic intracardiac electrograms are sensed of the left and right ventricles. The delay is determined by detecting peaks of the sensed intrinsic ventricular depolarizations and calculating the delay between the detected peaks of the intrinsic ventricular depolarizations sensed from the left ventricular and the right ventricles. Additionally, the duration of the QRS complexes are determined from either intracardiac electrograms or from surface ECG recordings.
The selection of one or more ventricular chambers then includes selecting one or more ventricular chambers in which to provide pacing pulses based on the duration interval of the QRS complex and the delay between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations. For example, in selecting one or more ventricular chambers, a suggestion to pace in a left ventricle is made when the duration interval of the one or more QRS complexes is greater than or equal to a first threshold value and the difference between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations is greater than a second threshold value. In one embodiment, the first threshold value is 120 millisecond and the second threshold value is zero (0). Alternatively, in selecting one or more ventricular chambers, a suggestion to pace in both the left ventricle and the right ventricle is made when the duration interval of one or more QRS complexes is greater than or equal to the first threshold value and the difference between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations is greater than the second threshold value. Finally, in selecting one or more ventricular chambers, a suggestion to pace in a right ventricle when the duration interval of one or more QRS complexes is greater than or equal to the first threshold value and the difference between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations is less than or equal to the second threshold value. In one embodiment, this suggestion is made through the use of either an implantable pulse generator and/or a medical device programmer.
In one embodiment, the apparatus of the present subject matter includes at least one receiver, where the receiver receives intrinsic intracardia electrograms from the left ventricle and the right ventricle. These electrograms include a left ventricular and a right ventricular sensed intrinsic ventricular depolarizations having QRS complexes. In an additional embodiment, the receiver receives the QRS duration interval of one or more QRS complexes measured from a surface ECG.
The apparatus further includes a controller, where the controller determines a timing relationship between intrinsic electrograms recorded from the left and right ventricle. In one embodiment, the controller calculates a delay between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations and is adapted to receive a duration interval of one or more QRS complexes. In one embodiment, the QRS duration interval is provided to the controller from measurements made from a surface ECG recording. In an alternative embodiment, the controller determines the duration interval of the QRS complexes from the sensed cardiac signals.
The apparatus further includes a ventricular chamber selector. The ventricular chamber selector selects one or more ventricular chambers in which to provide pacing pulses based on the timing relationship between intrinsic intracardia electrograms recorded from the right and left ventricle. In one embodiment, the ventricular chamber selector selects one or more ventricular chambers in which to provide pacing pulses based on the duration interval of the QRS complexes and the delay between the left ventricular and the right ventricular sensed intrinsic ventricular depolarizations, as described above. The apparatus of the present subject matter can be incorporated into a medical device programmer and/or an implantable pulse generator, where the implantable pulse generator includes a first cardiac lead and a second cardiac lead, where the first and second cardiac leads each include electrodes for sensing the intrinsic intracardia electrograms from the left ventricle and the right ventricle.